This invention relates generally to an electrode assembly for attachment to body tissue to sense electrical heart activity. The electrode is particularly suited for insertion through the vaginal passageway of a woman in labor and for remote controlled attachment to the fetus; specifically, the head (scalp) of the fetus. The electrode provides heart signals to electronic monitoring equipment which display an EKG (electrocardiogram) signal and/or the heart rate.
In general, a remote control device for screwing a retaining coil electrode into the scalp of the fetus is shown in a number of patents, including Hon, et al., U.S. Pat. No. Re. 28,990. Here a flexible drive carries the fetal engaging electrode and is rotatably disposed within a rigid guide tube.
The proximal end of the flexible drive engages a fin on the back of the electrode holder so that when rotation is applied to the distal end of the drive (by the hand of the surgeon) rotation is transmitted to a spiral electrode which is screwed into the fetal epidermis. Thereafter, the entire drive and guide tube assembly is removed allowing the electrode to remain attached with wires going to a suitable monitoring system, and then the delivery of the child may proceed.
Other patents offer alternative methods of applying rotating force to a spiral electrode or different means therefor.
Murphy U.S. Pat. No. 4,180,080 employs a single flexible guide and a handle connected to the twisted electrode leads which are threaded through the guide tube and which are attached to the scalp engaging electrode. When the handle is rotated, this rotary motion is imparted to the spiral electrode by means of the electrode leads driving it into the fetal epidermis; here the flexible guide tube remains stationary. Since the guide tube of Murphy is flexible, it is difficult to obtain the forward force necessary to penetrate the fetal epidermis. It is also difficult to obtain a positive drive force due to the inherent flexibility of the twisted wires.
Another technique of an applicator employing a plunger at the distal end of a guide tube and means for converting the linear motion generated by depressing the plunger to rotary motion is shown in Hon U.S. Pat. No. 4,321,931; and Helfer, et al., U.S. Pat. Nos. 4,301,806, and 4,437,467. These have not received wide acceptance due to the complexity of the design and the high cost of manufacture. Furthermore, the user cannot be sure of proper electrode attachment when the plunger is depressed. Further, these designs either employ a rigid guide tube of fixed curvature or a flexible guide tube which lacks the rigidity necessary to apply forward force to the fetal engaging electrode.